The present invention relates to a method and to an arrangement for mutually bonding at least two moving continuous webs of material. The invention also relates to a disposable absorbent article, such as a diaper, a sanitary napkin, an incontinence guard or the like which includes an absorbent pad, a liquid-impermeable layer on one side of the pad and a liquid-permeable, liquid-receiving outer layer on the other side of the pad, said outer layer including at least two mutually bonded liquid-permeable layers.
Methods for mutually bonding two or more moving material webs to form an essentially smooth laminate are known in the art. According to one such known method, the material webs are thermobonded between two heated, rotating rolls. According to another method, a binding agent is applied to at least one of the webs, whereafter the webs are combined and bonded to one another, for instance by passing the webs between two rolls. Another known method involves laminating two material webs with the aid of ultrasonic welding techniques. A prerequisite for both thermobonding and ultrasonic welding is that at least one of the webs includes weldable material. In these cases, the webs are comprised, for instance, of non-woven fabric comprising fibres of, for instance, polyethylene, polypropylene, polyester or the like. Webs of thermoplastic films are another example of such material webs.
The European Patent Application EP-A-0 409 315 teaches a method of producing a laminate which includes at least one corrugated laminate layer. Two laminate layers, of which at least one has corrugations in the movement direction of the layer, are passed through the nip of two rolls of which at least one has a plurality of peripheral grooves in which the corrugations are intended to fit while the layers are mutually bonded in regions located between the corrugations, i.e. in regions corresponding to the spaces between the grooves in the roll or rolls. According to this known laminating method, it is important that the corrugations are not displaced laterally so as to leave the grooves, i.e. to lie completely or partially between the grooves in the roll or rolls. If this should happen, wrinkles are formed in the laminate and which is said to be unsatisfactory.
It is also known from the so-called MICREX process, proposed by Micrex.RTM. Corporation, to microcr epe material webs that are comprised, for instance, of non-woven fabric. This process, however, is not concerned with mutually joining two material webs, and the microcr eping process is carried out on a single layer, or on a laminate, comprised for instance of non-woven fabric. Microcr eping can be likened to microscopic wrinkling of the material web transversely to its movement direction. However, the durability of the wrinkles in the web in a continued manufacturing process is highly uncertain. In one diaper manufacturing process for instance, the web is subjected to significant tensile forces in the process direction of the web and the diaper manufacturing machine. Since the wrinkles are not permanently set, there is a serious risk that the wrinkles will be smoothed-out when the web is subjected to forces in its longitudinal direction. Furthermore, if the microcr eped material webs are rolled-up on a rack after the microcr eping process and before being used in the diaper manufacturing process, the wrinkles may be influenced unfavourably, e.g. may be smoothed-out and disappear.